The present invention relates to an automatically engageable jaw or dog clutch.
Generally speaking, the automatically engageable jaw clutch or dog of the present development is of the type comprising a toothed drive hub and a toothed power take-off hub. There is also provided an axially displaceable clutch star which is rigidly connected for rotation with the drive hub by means of a first tooth system or set of teeth formed at the clutch star, however is connected to be axially displaceable. The clutch star possesses a second tooth system or set of teeth which can be brought into engagement with the tooth system or set of teeth of the power take-off hub by axially displacing the clutch star. A screw socket is rotatably mounted at the clutch star. This screw socket is connected by means of a pair of coarse-pitch threads with the power take-off hub. The clutch star entrains, in one rotational direction, the screw socket by means of a pawl blocking device composed of pawls and a pawl tooth system. A bearing serves to support the drive hub and power take-off hub against one another. Additionally, there is provided a channel system for a lubricant which flows under the action of the centrifugal forces through the jaw or dog clutch, the bearing being supplied with fresh lubricant from a central inlet or flow channel.
According to a state-of-the-art jaw or dog clutch of this type, as disclosed for instance in U.S. Pat. No. 3,563,354, granted Feb. 16, 1971, and the cognate Swiss Pat. No. 499, 735 and German Pat. No. 1,959,184, the bearing, by means of which there are mutually supported the drive hub and the power take-off hub, is arranged axially externally of the space enclosed by the drive hub, the clutch star or spider and the screw socket between a central drive shaft attached to the drive hub and a hollow shaft secured at the power take-off hub. The central inlet channel extends from the end of the drive shaft attached at the drive hub through such drive hub and terminates at radial channels in the drive shaft which, in turn, open at a guide bushing enclosing the drive shaft with radial clearance. The guide bushing is attached by means of a flange at the power take-off hub and is provided at its outer surface with a cylindrical guide surface at which there is displaceable the screw socket. Machined at the guide bushing are two sets of radial channels arranged at an axial spacing from one another, both of these sets of radial channels terminating at the cylindrical guide surface for the screw socket. Circumferentially about the guide surface the screw socket is provided with two grooves or recesses arranged at an axial spacing from one another, which are connected with the pawl teeth and the coarse-pitch threads of the screw socket or spider by channels machined therein. With the clutch disengaged the screw socket assumes a position where its grooves or recesses enclose the channels in the guide bushing, so that the lubricant oil can flow from the central inlet or inflow channel through the guide bushing and through the screw socket, on the one hand, to the pawl blocking device and, on the other hand, to the pair of coarse-pitch threads and from that location further to the teeth of the clutch star and the drive hub and power take-off hub. During engagement of the jaw clutch the screw socket is screwed towards the power take-off hub, and both of its grooves or recesses are separated from the channels of the guide bushing, so that there is interrupted, on the one hand, the direct lubricant supply of the pawl blocking device and, on the other hand, the pair of coarse-pitch threads by the screw socket. However, a set of channels in the guide bushing is completely freed by the screw socket, so that the lubricant now predominantly reaches the continuously meshing teeth of the drive hub and the clutch star, between which there can arise continuous relative movements, when the clutch is engaged, owing to axial alignment errors of both shafts which are coupled with one another. Independent of whether the prior art jaw or dog clutch is engaged or disengaged, a portion of the lubricant which arrives through the central inlet channel into the interior of the jaw clutch flows outwardly through the bearing. This portion of the lubricant is then no longer available for the lubrication of the remaining parts or components of the jaw clutch. It is therefore necessary to ensure, by means of an appreciable excess of lubricant conveyed by an external pump, that the pawl blocking device, the pair of coarse-pitch threads and the teeth of the jaw clutch also will be then sufficiently lubricated if, with gradually increasing bearing temperature which arises during operation, an increasingly greater part of the lubricant outflows through the bearing. However, this means that during certain operating conditions, for instance with relatively cold bearing, the mentioned remaining parts or components of the jaw clutch will have an excessive amount of lubricant flowing therethrough. Hence, in particular, with disengaged jaw clutch, on the one hand, there can arise increased power losses, and, on the other hand, however there is not ensured at all for an adequate supply of all of the part or components with fresh, cooled lubricant, since in certain hollow spaces of the clutch there can arise a dam-up phenomenon where the lubricant tends to excessively heat-up.